Variable resistance



Patented Sept. 4, '195i I l"UNITED As 'l'ir'rlss PATENT oFFicE gvAmlzsltz;;STANCl I Benjamin n."sam, seaman, s. Lautner,

toGeneralElec NewYork tric Company, a corporation of Application aum 21,isis, serial No. 112,122

. l y l invention 'relates to variable resistances, and moreparticularly to precision variable-resistances of the type in which theresistance'wire is wound i'n turns on 'a `suitable support and anelectric contact is moved' over bared portions of tbe turns to vary theportion of the resistance included in an electrical circuit, and hasfor'its object means for reducing the resistance value of the steps inthe change of the resistance as the contact'moves over the turns and foraveraging variations in the resistance of the wire.

In the simplest form of variable resistance, which is a straight wirewith a movable contact or brush, any desired change in resistancevariation can be obtained as a function of the brush movement. Howeveixwhen this same wire is wound on a suitable support in a plurality ofturns with a brush sliding over the turns, the resistance obviouslychanges in steps with 'brush movement. the value of each step being theresistance f a turn upon movement of the brush from one turn to theother. A reduction in value of resistance steps may'be obtained bysuitably increasing the'length of the turn wound resistance so as todecrease the resistance of each turn but that is unsatisfactory whencompactne'ss is required. Accordingly, a further object of the inventionis 4a reduction in the step by step resistance change with brushmovement while retaining the advantage of a short, compact re-V sistanceunit.

Another disadvantage of turn wound resistances is that the unit lengthresistance of the wire itself varies becauseof manufacturing variationsin the diameter of the wire and, accordingly, another object of myinvention is to average substantially such variations in the resistanceof the In carrying out my invention in one form, I provide at least twospaced apart brushes for a turn wound resistance, .which brushes areconnected in parallel with a resistance in series with at least onebrush and spaced apart a. distance sutlicient to include between them aplurality of the turns o! the resistance suillcient to averagetheinherent wire resistance variations. For minimum step by step resistancechange, it is desirable'that the' currents in the brushes besubstantially equal and, accordingly, in one form 'of my invention-whentwo brushes are used, I

single brush.

ll'or a more complete understanding of my invention,- reference shouldbe had to the accompanyi'ng drawing, Fig. l of which is a diagrammaticrepresentation of a wound resistance unit l1 Claims. (CL lOl-42) withtwo brushes embodying my invention: Fig. 2 is an enlargedfragmentaryview showing the relative arrangement of the brushes; Fig. 3"shows a--modiiied-form -of my invention utilizing brushes in spacedrelation with each other; while Figs. 4 and 5 are modified formsshowingfthe application of my invention to potentiometer resistancesutilizing, respectively'gtwo and three bmsn'es. v

Referring to the drawing; in Fig. 1 the resistance wire i! is wound inturns/on an electrical insulating 'support or card Ii shown as a stripof suitable rigid electrically insulating material. such as a plastic orfiber material; Although the wire turns extend around,thc support, itwill be understood that other tumshapes may be used such' as pass back'and fortlrjon one side of the-support. -For variation of the' amount ofthe resistance included in an electric circuit of which the conductorsi2 and il 'form a part, two electric contacts, shown as brushes-.ll andII, are provided which engage bared portions of the turns on the upperedge, as shown, ofthe resistance unit. The brushes Il and ii aresuitablymounted on an electrically insulatinfgsupport'li which is movable inpredetermined spaced parallel relation with the upper edge 'of 'theresistance unit so that the brushes, shown as made of a suitable tionshaving a diameter greater, and hence lower resistance,'than normal, thusproducing plus and minus deviations from a desired linear outputcharacteristic. Their Ainclusion in series between the two brushes inparallel with the resistance 2l has the effect of averaging theresistance variations at the brush contact points so that the resistanceoutput at connection llfi'naterially improves linearity of the outputcharacteristic of the unit. In a resistance 'wound-of .0015 inchdiameter-wire, for example, the number of turns included between thebrushes may be 500.

In precision wound resistors .each turn is exactly spaced from thepreceding turn to given the' desired resistance characteristics withrespect to the brush movement with consequent unequal spacing of theturnsA as turngresistan'ces vary. Because of this unequal spacing' ofthe turns. the brushes ordinarily do not each short circuit a turn atthe same time-and, consequently, the resistance of the wire betweenothebrushes remains "substantially constant. This condition is shown in Fig.2 of the drawing. in which the brush I i is about to move into the spacebetween the turn portions II and I l upon further movement toward theright hand, as seen in the draw-` Ing, thereby to short circuit the turnbetween the portions I'I and Il while, at the same time, the brush I4obviously maintains its engagement with the turn or portion I9. It willbe obvious from` the'above description in connection with Fig. 2 thatthe ideal spacing between brushes Il and I l would be a spacing distanceequal to an integral multiple of the anticipated `average resistor turnspacing plus one-half of the anticipated turn spacing in order that thebrushes Il and Il be completely "out of phase in their travel across theresistor wire turns. Likewise, with the embodiments of Figs. 3 and 5,involving the use of three brushes, the ideal spacing would include aone-third turn spacing and for a larger 'number of brushes thefractional turn spacing being connected electrically to the conductorI2.

In the two-brush arrangement of Fig. 1, this resistance should be equalto the resistance between the brushes I4 and I5. It will be noted thatthe wire resistance between the brushes I4 and Il is connected inparallel with the resistance 20. With this arrangement, the resistancesteps are reduced to the equivalent of one-half turn, because each turnis carrying one-half current in the parallel circuit. When each turn isadded to the`circuit between conductor I3 and brush M, its currentdoubles, with consequent one-hall' turn resistance increase effect.

In the arrangement of Fig. 3, we have shown the use of three brushes, 2I, 22 and 23, secured on a movable insulating support 24 so that the twooutside brushes engage the resistance unit 25 in equally spaced relationwith the central brush. In this case the values of resistors 23 and 21-are again chosen for equal brush current division. With `thisarrangement, the current increases one-third in each turn as it isincluded in the circuit and ,each resistance step is reduced toone-third ascompared to a single brush.

In Figs. 4 and 5, I have shown suitable arrangements for use withpotentiometer resistance units where the direction of current ow throughthe resistance unit to the brushes may not always be the same or wherebrush current is of negligible magnitude. In Fig. 4, the resistances 28and 23 .may 4be equal, respectively, to substantially onehalt theresistance between the brushes 30'and 3|, attaining a reduction inresistance steps in a manner similar to that described above. Theresistances 2l and 29 have a voltage take-of! point at their commonconnection, wire 32.

In the three-brush arrangement shown in Fig. 5, the resistances 33, 34,and 35 may be each substantially' equal to one-half the resistancebetween the two outside brushes 36 and 31, the two outside brushes beingequally spaced from the central brush. It will be understood that in theembodiments. of Figs. 4 and 5 the brush resistances 28,129, and. 33, 34,and 35 may advantageously be o f higher resistance values than thosestated, although the resistance values stated have been found to givesatisfactory results and they should be taken as recommended minimumresistance values.

While I have shown a particular embodiment of my invention, it will beunderstood, of course, that I do not wish to be limited thereto sincemany modiilcations may be made and I therefore contemplate, by theappended claims, to cover any such modifications as fall within the truespirit and scope of my invention.

What! claim as new and desire to secure by Letters Patent -of the UnitedStates is:

1.l A variable resistor comprising a resistance wire wound in aplurality of turns on a support, a :pairv of electric contacts, meansfor supporting said contacts in spaced relation with each other incontact with saidy resistance wire, said support being movable` alongsaid resistance wire thereby to move said contacts over said turns,electric connections for connecting said contacts together, a resistanceincluded in said connections with at least one of said contacts, saidelectrically interconnected contacts together comprising one outgoingresistor connection.

2. A-variable resistor comprising a resistance wire wound in a pluralityof turns on a support, a plurality of electric contacts, means forsupporting said contacts in spaced relation with each other in contactwith said resistance wire, said support being movable along saidresistance wire thereby to move said contacts over said turns. electricconnections for connecting said contacts together, and resistancesincluded in saidconnections with said contacts 'having values such as to'maintain substantially equal currents in said contacts, saidelectrically interconnected contacts together comprising one outgoingresistor con- A nection.

3. A variable resistor comprising a resistance wire wound in a pluralityof turns on a support, a fixed outgoing connection at one end of saidwire, a pair of, electric contacts, means for supsaid wire between saidcontacts so as to maintain: substantially equal currents in saidcontacts."' `y 4. A variable resistor comprising a resistance wire woundin a plurality of spaced turns on a support, a pair of contacts, meansfor supporting said contacts in spaced relation with each other incontact with said resistance wire, said support being movable along saidresistance wire thereby to move said contacts over said turns, saidcontacts being mounted on said support in such spaced relative positionsas to average variations in the resistance of said wire between saidcontacts, electric connections ior .connecting saidl lcontacts together,and `a resistance included in wire wound in a plurality of spaced turnson aI support, a plurality of electric contacts, means for supportingsaid contacts in spaced relation` with each other in contact with saidresistance wire, said support being movable along said resistance wirethereby to move said contacts over said turns, said contacts beingmounted on said.

support in such spaced relative positions as to average variations inthe resistance of said wire between said contacts, electric connectionsfor connecting said contacts together to form a movable outgoingresistor connection, and resistances included in said connections withsaid contacts having values such as to maintain substantially equalcurrents in said contacts.

6. A variable resistor comprising a resistance wire wound in apluralityoi spaced turns on a support, a ilxedvoutgoing connection atone end of said wire, a pair of electric contacts, means for supportingsaid contacts in spaced relation with each other in contact with saidresistance wire, said support being movable along said resistance wirethereby to move said contacts over said turns, said contacts beingmounted on said support in such spaced relative positions as to averagevariations in the resistance of said wire between said contacts,electric connections for connecting said contacts together, and aresistance included in said connections with the one of said contactsnearest said fixed outgoing connection having a value substantially thesame as the value of the resistance of said wire between said contactsso as to maintain substantially equal currents in said contacts therebyto reduce the effective resistance step to substantially onehalf turn.

7. A variable resistor comprising at least one iixed outgoing terminaland one movable outgoing terminal, said movable outgoing terminal beingconnected to a plurality of electrically and mechanically interconnectedresistor contact brushes, said electrical interconnections includingcurrent-limiting resistors.

8. A resistance wire wound electrical resistor .having a movable contactdevice comprising a plurality o1' mechanically and electricallyinterconnected contact brushes for contacting axially closely spacedpoints on said resistor, said electrical interconnections includingelectrical resistance, and an outgoingterminal connected to said movablecontact device.

9. A movable contact terminal device for a resistance wire woundelectrical resistor, said device comprising at least two contactbrushes, said brushes being both mechanically and electricallyinterconnected, said electrical intercon- 6 nection including electricalresistance, said brushes being axially spaced bya distance equal to anintegral multiple of the anticipated average resistor turn spacing plusa fractional portion thereof, the fraction having a denominator equal tothe number of brushes.

10. A movable contact structure for establish ing an outgoing connectionfor a resistance wire- Wound electrical resistor comprising a pluralityof contact brushes for contacting the windings of said resistor,resistors connected in series with a number of said brushes at least asgreat as one less than the total number of said brushes, said brushesbeing mechanically connected and spaced from one another by distancesequivalent to whole multiples of the anticipated average resistor turnspacing plus fractional multiples of said spacings, said fractionalmultiples comprising a fraction whose denominator is equal to the numberof said brushes.

11. A resistance wire wound electrical resistor having a fixed outgoingconnection at one end thereof, a movable outgoing connection contactnection, the higher value resistors being connected to the closerbrushes.

BENJAMIN B. SCO'I'I.

REFERENCES CITED The following references are of record inthe ille ofthis patent: Y

UNITED STATES PATENTS OTHER REFERENCES zeitschrift Fur Instrumenenkunde.vol. 34, 1914, pages 142-151.

